Traditional Manufacturing Processes

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Traditional Manufacturing Processes
Casting
Forming
Sheet metal processing
Powder- and Ceramics Processing
Plastics processing
Cutting
Joining
Surface treatment
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FUNDAMENTALS OF METAL FORMING

• Overview of Metal Forming
• Material Behavior in Metal Forming
• Temperature in Metal Forming
• Strain Rate Sensitivity
• Friction and Lubrication in Metal Forming

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Metal Forming

• Large group of manufacturing processes in which
  plastic deformation is used to change the shape
  of metal workpieces
• The tool, usually called a die, applies stresses
  that exceed yield strength of metal
• The metal takes a shape determined by the
  geometry of the die

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Stresses in Metal Forming

• Stresses to plastically deform the metal are
  usually compressive
• Examples rolling, forging, extrusion
• However, some forming processes
• Stretch the metal (tensile stresses)
• Others bend the metal (tensile and compressive)
• Still others apply shear stresses

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Material Properties in Metal Forming

• Desirable material properties
• Low yield strength and high ductility
• These properties are affected by temperature
• Ductility increases and yield strength decreases
  when work temperature is raised
• Other factors
• Strain rate and friction

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Bulk Deformation Processes

• Characterized by significant deformations and
  massive shape changes
• "Bulk" refers to workparts with relatively low
  surface area-to-volume ratios
• Starting work shapes include cylindrical billets
  and rectangular bars

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Basic bulk deformation processes (a) rolling
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Basic bulk deformation processes (b) forging
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Basic bulk deformation processes (c) extrusion
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Basic bulk deformation processes (d) drawing
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Material Behavior in Metal Forming

• Plastic region of stress-strain curve is primary
  interest because material is plastically deformed
  
• In plastic region, metal's behavior is expressed
  by the flow curve

• where K strength coefficient and n strain
  hardening exponent
• Stress and strain in flow curve are true stress
  and true strain

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Flow Stress

• For most metals at room temperature, strength
  increases when deformed due to strain hardening
• Flow stress instantaneous value of stress
  required to continue deforming the material

where Yf flow stress, that is, the yield
strength as a function of strain
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Temperature in Metal Forming

• For any metal, K and n in the flow curve depend
  on temperature
• Both strength and strain hardening are reduced at
  higher temperatures
• In addition, ductility is increased at higher
  temperatures

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HOT and COLD WORKING
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HOT and COLD WORKING

• Cold working is metal forming performed at room
  temperature.
• Advantages better accuracy, better
  surface finish, high strength and hardness of the
  part, no
• heating is required.
• Disadvantages higher forces and
  power, limitations to the amount of forming,
  additional
• annealing for some material is
  required, and some material are not capable of
  cold working.
• Warm working is metal forming at temperatures
  above the room temperature but bellow the
  recrystallization one.
• Advantages lower forces and power,
  more complex part shapes, no annealing is
  required.
• Disadvantages some investment in
  furnaces is needed.
• Hot working involves deformation of preheated
  material at temperatures above the re
  crystallization temperature.
• Advantages big amount of forming is
  possible, lower forces and power are required,
  forming
• of materials with low ductility, no work
  hardening and therefore, no additional annealing
  is required.
• Disadvantages lower accuracy and surface
  finish, higher production cost, and shorter tool
  life.

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Friction in Metal Forming

• In most metal forming processes, friction is
  undesirable
• Metal flow is retarded
• Forces and power are increased
• Wears tooling faster
• Friction and tool wear are more severe in hot
  working

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Lubrication in Metal Forming

• Metalworking lubricants are applied to tool-work
  interface in many forming operations to reduce
  harmful effects of friction
• Benefits
• Reduced sticking, forces, power, tool wear
• Better surface finish
• Removes heat from the tooling

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Considerations in Choosing a Lubricant

• Type of forming process (rolling, forging, sheet
  metal drawing, etc.)
• Hot working or cold working
• Work material
• Chemical reactivity with tool and work metals
• Ease of application
• Cost

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Definitions

• Plastic Deformation Processes
• Operations that induce shape changes on the work
  piece by plastic deformation under forces applied
• by various tools and dies.
• Bulk Deformation Processes
• These processes involve large amount of
  plastic deformation. The cross-section of
  workpiece changes without volume change. The
  ratio cross-section area/volume is small. For
  most operations, hot or warm working conditions
  are preferred although some operations are
  carried out at room temperature.
• Sheet-Forming Processes
• In sheet metalworking operations, the
  cross-section of work piece does not changethe
  material is only subjected to shape changes. The
  ratio cross-section area/volume is very high.
• Sheet metalworking operations are
  performed on thin (less than 6 mm) sheets, strips
  or coils of metal by means of a set of tools
  called punch and die on machine tools called
  stamping presses. They are always performed as
  cold working operations.

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Bulk Deformation Processes

• Rolling Compressive deformation process in which
  the thickness of a plate is reduced by squeezing
  it through two rotating cylindrical rolls.
• Forging The workpiece is compressed between two
  opposing dies so that the die shapes are imparted
  to the work.
• Extrusion The work material is forced to flow
  through a die opening taking its shape
• Drawing The diameter of a wire or bar is reduced
  by pulling it through a die opening (bar drawing)
  or a series of die openings (wire drawing)

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Rolling

• Definition
• Rolling is a Bulk Deformation Process in
  which the thickness of the work is reduced by
  compressive forces exerted by two opposing rolls

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Rolling
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Rolling
Important Applications Steel Plants, Raw
stock production (sheets, tubes, Rods,
etc.) Screw manufacture
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Rolling Basics
Sheets are rolled in multiple stages (why ?)
Screw manufacture
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Forging

• Definition
• Forging is a Bulk Deformation Process in
  which the work is compressed between two dies.
  According to the degree to which the flow of the
  metal is constrained by the dies there are three
  types of forging
• ? Open-die forging